用于木质纤维素选择性分离的深共熔体系的构效关系和分子模拟

Deep Eutectic Solvents (DES) are new solvent systems similar to ionic liquids, which are perpared by mixing two high-melting-point materials, forming room temperature liquids via hydrogen bonds. It is potential solvent in the pretreatment of lignocellulose with advantages of low-cost, easy-to-preparing and environmental friendly. In this work, we developed three qualitative indexes to reflect the ability of DES in dissolving different species in lignocellulose. ① Structure and energy of hydrogen bonds between various monomers and DES are calculated by quantum methods; ② The two-dimensional distributions of distance-angle and distance-energy of hydrogen bonds between components of lignocelluose and DES by bulk phase molecular simulation. The hydrogen bonds are studied in different types of the lignocelluose components dissolved in DES, including monomers, oligomers, crystal and amorphism, by which some clue to the solubility is obtained. ③ The infinite dilute activity coefficients are obtained by COSMO-RS method. These different indexes can not only be used in screening new DESs, but also helpful to understand the mechanism of dissolution of lignocellulose.

深共熔溶剂（Deep Eutectic Solvents, DES）是一类与离子液体非常相似的新型溶剂，由两种较高熔点的物质通过混合形成氢键降低熔点得到，将其用于木质纤维素预处理过程，具有成本低、制备简单和环境友好等优点。本项目从木质纤维素各基本单元的分子结构出发，结合量子化学计算、分子模拟和COSMO-RS模型建立并比较三种定量指标，用于评价DES选择性分离木质纤维素的性能。①小分子复合物间的氢键；②基于分子模拟得到氢键距离/角度和距离/能量的二维分布，对DES溶解木质纤维素中不同组分时形成的氢键网络，采用从简单到复杂（单体-寡聚物-晶体和无定形表面）层层推进开展模拟，对不同层次溶质的氢键结构和能量考察其相应变化，在氢键与溶解度之间建立关联。③基于COSMO-RS预测无限稀释活度系数。这些定量指标不仅可用于筛选新型DES，也有助于理解木质纤维素的溶解机理。

本项目针对低共熔溶剂体系，采用多尺度模拟方法建立有效关联，以便为大规模溶剂筛选奠定基础。主要成果有：1）确定了采用M06-2X/6-311++G(d,p)水平的量化计算能够在适中的计算量下获得足够准确的结果；通过约化密度梯度分析能够精准表征分子间较强的弱相互作用；建立了键临界点处的电子密度（ρBCP）与相互作用能之间的半定量关联，从而可以实现更大体系作用能的估算。2）利用文献发表的使用数据，对COSMO-RS方法预测准确度进行了系统验证，发现对于醇类体系该模型预测的lnγ∞偏差在±1之间，尚不能达到定量预测水平，但可以用于大规模的初步筛选。提出一种新的基于分子团簇（dimer）的产生σ-profile的方法，能够改善COSMO-RS定量预测的结果。3）利用粗粒化的非平衡分子动力学模拟对相界面传质过程开展研究，发现液液界面的局部密度显著小于体相，形成一个自由能势阱，导致溶质首先在界面富集，而传质过程则需要填平该势阱才能实现。这一结果有助于从分子层面改进经典的双膜理论。4）确定了获取准确溶解度数据的实验条件，采用静态法测定了葡萄糖和纤维二糖在几种低共熔体系中的溶解度，结果表明DES体系对于生物质的溶解能力远远不如离子液体。